In recent years, as portable information terminals which are referred to as notebook personal computers and PDAs (Personal Digital Assistants), are spread, a wireless data communication in which an electrical or optical wire is not required, is frequently used as a data communication between information terminal devices. As a system of wireless data communication, there is a data communication using the infrared rays.
The infrared data communication system is standardized by the IrDA (Infrared Data Association). It is possible to carry out a data transmission between information terminal devices at a communication speed of about 100 kbps to 4 Mbps. Further, in recent years, the IrMC (Infrared Mobile Communications) which is an infrared communication standard for a portable telephone, the IrOBEX (IrDA Object Exchange) which is an infrared object exchange protocol, the IrDA Lite for using the infrared communication in a small device, and the like are standardized. It is possible to realize a flexible and high performance infrared communication between terminal devices.
In such a technical background, the infrared communication has been widely used to exchange data between information terminal devices. However, at present, the infrared communicating function is not necessarily provided on each portable telephone. Therefore, the data communication using the infrared rays between all of the information terminal devices, such as between a portable telephone, a personal computer and a PDA or the like, is not always carried out.
In recent years, as portable information terminals which are referred to as notebook personal computers and PDAs (Personal Digital Assistants), have become more popular, a wireless data communication in which an electrical or optical wire is not required, is frequently used as a data communication between information terminal devices. As a system of wireless data communication, there is a data communication using the infrared rays.